Separation vessels are used in various fields, for instance to separate solid particles from liquid particles in a slurry. One such field is bitumen extraction from mined oil sands.
Processes for extracting bitumen from mined oil sands commonly employ the steps of bitumen extraction, bitumen froth separation, and froth treatment. An example of such a process will now be provided, although different processes exist.
Oil sand is supplied from a mine, mixed with water, and separated from rocks and debris. The slurry is conditioned by adding air, and optionally chemical additives such as caustic (sodium hydroxide). Conditioning serves to liberate the bitumen from the oil sand and aerate the bitumen to produce buoyant bitumen droplets. The slurry is sent to a primary separation cell/vessel (PSV) where the aerated bitumen droplets separate from most of the solids to form bitumen froth. PSV's are typically large conical gravity separation vessels designed to provide a sufficient residence time in a low mixing energy environment to allow buoyancy forces to separate the bitumen froth and sand from the slurry. The slurry is supplied to the PSV through a feed pipe at sufficient velocity to limit solids deposition and this flow enters a central feedwell where it is distributed radially into the vessel. Lighter bitumen droplets rise through the froth underwash layer and accumulate in the froth layer at the top of the vessel where it overflows a weir and is sent for further processing. A supplementary hot water underwash flow is supplied under the bitumen froth layer to assist with removal of fine solid particles and to increase froth temperature. The fine, near neutral buoyancy particles tend to be suspended in the middlings zone of the vessel and are either drawn with the middlings stream to flotation or pumped away in an underflow stream.
The bitumen froth product stream from the PSV comprises bitumen, water and fine solids (also referred to as mineral solids). A typical composition of bitumen froth is about 60 wt % bitumen, 30 wt % water, and 10 wt % solids. This froth is then treated to separate out diluted bitumen. The tailings stream from the PSV comprises coarse solids, some fine solids, and water.
Thus, PSVs typically employed in water-based oil sand separation systems are used to separate bitumen and solids in a three-phase separation process. Preferably, the PSV should provide high recovery of bitumen froth, clean bitumen froth (with low solids concentration), low wear leading to low maintenance, and good performance over the range of expected operating conditions. To meet these performance goals, the central feedwell should take the varying incoming feed stream and distribute it evenly in all azimuthal directions and minimize mixing motions that would disturb the underwash water layer.
One known PSV feedwell is the Syncrude Aurora feedwell design described in Tyler, J., Spence, J. Kiel, D., Schaan, J. Larson, G. (2009) “The Use of Physical Modeling in the Optimization of a Primary Separation Vessel Feedwell”, The Canadian Journal of Chemical Engineering, and shown in FIGS. 1A and 1B herein. With reference to FIGS. 151A and 1B, a feed inlet (101) enters tangentially into an open barrel (102) which allows excess air to escape. The flow swirls through the barrel with eight radial baffles (103a, 103b, 103c, 103d, 103e, 103f, 103g, and 103h) of increasing size in the direction of the swirl. The flow discharges from an orifice at the bottom of the barrel (104), and through a short downpipe (105) onto a conical deflector plate (106).